Biology Projects

The effects of tetrodotoxin concentraion on cutanous bacterial communitites in the rough skinned newt (Taricha granulosa)

Dr. Kathy Szick and Dr. Amber Stokes

Worldwide, amphibian populations have been in decline. One source of this decline is fungal pathogens, most notably Batrachochytrium dendrobatidis, commonly referred to as Chytrid fungus. This fungus is widespread and has devastated populations of many amphibian species. One particular group of amphibians that has had relatively little impact from chytrid fungus is the western newts. Western newts are a group of salamanders found in the western United States that is composed of four species. Each of these species produces a toxin known as Tetrodotoxin (TTX). Tetrodotoxin is most commonly known as the toxin found in puffer fish, and is used by the salamanders as a defense against predators like snakes and birds. There is much variation in the levels of TTX within a species, between species, and between populations. Some species like the California newt (Taricha torosa) have relatively low levels of TTX in most populations, while species like the rough-skinned newt (Taricha granulosa) have been shown to have very high levels of TTX in some populations as well as low levels in others. Interestingly, rough-skinned newts have had few documented cases of infection by the Chytrid fungus, whereas the California newts have more often been documented with this infection. Some species of amphibians have been shown to have bacteria on their skin that produce antibiotics and antifungals protecting them from infection. Given the variation in TTX levels and the variation in the types of skin bacteria present on amphibian skin, we hypothesize that TTX levels impact the bacterial species present on the skin of these newts which may play a role in the ability to fight off infection from fungal pathogens like Chytrid fungus. This is a collaborative project where students will be working with Dr. Kathy Szick to identify bacterial variation associated with various next species and Dr. Amber Stokes to examine TTX levels. Students will learn basic lab techniques such as pipetting as well as plating and handling bacteria. Students will also gain experience using an immunoassay and challenge assays to quantify TTX and test the antifungal capabilities of the cutaneous bacteria from the newts, respectively. Finally, students will gain experience with techniques used to identify the genes of particular bacterial species such as Polymerase Chain Reaction (PCR) and Denaturant Gradient Gel Electrophoresis (DGGE).

Members of the bacterial genus Streptomyces are very common soil inhabitants. Most of them are saprophytes, meaning organisms that thrive on dead or decaying organic material. Although several hundred different species of Streptomyces have been identified, only several are plant pathogens. Streptomyces scabies is the dominant pathogenic species worldwide. It causes potato scab disease which leads to severe economic losses for the growers due to the unmarketability of their potato tubers. The main virulence factor of the bacterium is a plant toxin called thaxtomin A. This toxin inhibits cellulose biosynthesis in the plant cell wall, necessary for the plants to grow. Apart from being the main weapon of potato scab disease-causing streptomycetes, thaxtomin A can be used as a bioherbicide for controlling weed growth in agricultural and horticultural applications. Several large natural product companies are looking to put thaxtomin A on the market. However, Streptomyces scabies does not make this toxin under all conditions. It is for us to figure out what the best conditions for toxin production are and which genes exert control over this production. In the lab we will test different growth conditions, generate specific mutations in the bacterial DNA, and study the influence of these mutations on the production level of the toxin.

The green leaves of plants capture carbon dioxide from the air and use solar energy to turn it into carbohydrates. This process is arguably the most important chemical reaction on planet earth and the energy contained in these carbohydrates powers virtually all of the ecosystems of the globe. Because of its broad importance, understanding how photosynthesis works has been a major research objective for many years. Surprisingly, in spite of intense research focus, there are many aspects of photosynthesis that remain mysterious. The present study will examine leaf structural traits that are hypothesized to be important in photosynthesis. For example, cell wall thickness of leaf cells is predicted to affect photosynthetic rates based on the hypothesis that thicker cell walls leads to shading within a leaf that diminishes the amount harvestable light energy. To examine hypotheses about leaf structure and photosynthesis, 12 flowering plant species growing on campus at California State University, Bakersfield will be compared that broadly differ in their maximum photosynthetic rates. Maximum leaf photosynthesis will be measured using state-of-the-art equipment and quantified as carbon dioxide uptake rates of leaves. Leaf structure will be quantified using modern methods in microscopy, digital photography, and image analysis. Data will be analyzed by assessing correlations between photosynthetic rates and leaf structural traits. Results will provide mechanistic insights as to why some species have greater rates of photosynthesis than others.

The structure of plant water transport tissue in trees

Dr. Anna Jacobsen

Water is transported in plants through vascular tissue called xylem. Within the xylem water moves through special water conducting tubes composed of vessel element cells. The structure of xylem tissue and the water conducting cells are important determinants of tree water use and also impact the biomechanics of the wood of trees. This summer we will be conducting measures of the structure and anatomy of xylem tissue and vessel elements of poplar trees growing within a tree plot on the California State University, Bakersfield campus. We will also be measuring the biomechanics (strength and rigidity) of wood samples. This research is part of a multi-year funded grant project designed to examine xylem vessel structural traits as they relate to the xylem’s ability to efficiently and safely transport water. Although knowledge of xylem vessel structure and function is important in understanding plant water use and water transport, the structure of vessel networks remains little studied.

The petroleum fly, Helaeomyia petrolei, is a species of fly (Diptera: Ephydridae) endemic to California. The larvae feed on dead insects that become trapped in naturally occurring petroleum seeps. The petroleum fly is the only know species of insect that is able to spend the entirety of its immature stages developing in crude oil. Mature larvae exit the crude oil and undergo transformation to the adult stage in nearby vegetation surrounding the oil seeps. Little is known about the biology of the petroleum fly. In fact, the mating behavior and egg deposition have never been observed in nature; and no genetic studies have ever been published on the petroleum fly. The primary objective of this project is to conduct some preliminary genetic studies on the petroleum fly collected from three geographically isolated populations. Ultimately we will assess the within and among population genetic variation that exists between populations of the petroleum fly from Rancho La Brea, Santa Barbara, and Bakersfield, CA. We will also compare DNA sequences obtained from the petroleum fly to other Ephydrid sequences available on GenBank.